1. Field of the Invention
The present invention relates to a positioning apparatus.
2. Description of the Prior Art
Conventionally, there has been a positioning apparatus for a machine tool as shown in FIG. 11 (see Japanese Patent Laid-Open Publication No. 62-277245). The positioning apparatus is to position a turret head of a numerically controlled lathe where a shaft 102 of a turret head 101 is supported rotatably and axially movably at a support block 103, and a reduction gear 104 fixed to the rotary shaft 102 is connected via a gear 105 to a hydraulic motor 106 to rotate the turret head 101 by means of the hydraulic motor 106 and roughly position the turret head 101. There are further provided a positioning coupling (Curvic (trademark) coupling) 107 and 108 on mating faces of the turret head 101 and the support block 103, while the rotary shaft 102 is provided with a piston section 102a protruding radially from the rotary shaft 102. On the support block 103 are provided an oil chamber 103 a for receiving the piston section 102a and oil passages 103b and 103c for supplying oil from external to the oil chamber 103a to switch the oil supply direction to the oil chamber 103a by means of a directional control valve 109. Then, oil is supplied through the oil path 103b to move the turret head 101 rightward in FIG. 11 to thereby engage the teeth of the positioning coupling 107 and 108 with each other for the final positioning of the turret head 101, and the coupling is disengaged by supplying oil from the oil path 103c to the oil chamber 103a by switching the directional control valve 109.
However, since the above-mentioned conventional positioning apparatus employs a positioning coupling 107 and 108, it is necessary to axially move the turret head 101 each time positioning or rotating the turret head 101, which disadvantageously results in consuming much time in positioning as well as complication in construction. When the turret head moving speed is increased to reduce the time for movement, a severe impact takes place in coupling the positioning coupling 107, 108, which also incurs the problems of loud noise generation and reduction in lifetime of the apparatus. In the positioning coupling 107 and 108 which achieves coupling by mating the teeth thereof, production of backlash is not avoidable to be incapable of achieving high-accuracy positioning, which also results in limiting the position to be indexed.